Xin Fang

The pressure relief check valve plays a pivotal role in determining the oil and gas content during deep in-situ pressure-preserved coring. Prolonged exposure to high-pressure, high solid-content fluids in deep wells can lead to mechanical erosion of the check valve, potentially causing severe failure and a loss of sealing integrity. To withstand the typical f low conditions in shale gas wells and on the basis of an in-depth understanding of deep f luid dynamics, a check valve was designed to operate at 70 MPa pressure and relieve pressure after coring. To mitigate erosion, a coupled Computational Fluid Dynamics Discrete Element Method model was applied to simulate fluid flow dynamics and identify regions susceptible to erosion and wear in the valve body. The findings confirmed that the proposed check valve design meets the requirements for shale gas pressure-preserved coring and testing, with erosion mainly occurring in the constricted regions of the flow path. The erosion depth was found to increase with higher inlet flow rate and mass flow rates, demonstrating a sixfold increase as the inlet flow rate rises from 10 to 30 m/s. Non-spherical particles caused significantly more erosion than spherical ones, while the erosion depth decreased with larger particle sizes, showing a 33% reduction as particle size increased from 0.02 to 0.14 mm. To avoid sealing failures caused by prolonged erosion, the constricted flow channel was redesigned to accommodate an arc-shaped structure and appropriately widened. Simulations indicated that this structure can reduce peak pressure to 69% of the original value and minimize wall impacts. The maximum erosion depth decreased by 10%, indicating the improved durability and sealing of the redesigned check valve. These results underscore the enhanced check valve’s superior erosion resistance and sealing performance, highlighting its potential for future shale gas collection and testing and providing an effective strategy to enhance the reliability and longevity of check valves. Document Type: Original article Cited as: Fang, X., Li, C., Guo, D., Wang, D., Zhao, L., Xie, H. Novel structural design and anti-erosion performance evaluation of check valve applied to deep in-situ pressure-preserved coring. Advances in Geo-Energy Research, 2025, 15(3): 190-202. https://doi.org/10.46690/ager.2025.03.03

It is difficult to adapt traditional screw motors with rubber stators to the high-temperature and high-pressure conditions in ultra-deep wells, where rubber stators age, deform and carbonize, resulting in motor failure. In this study, the goal is to develop volumetric power drilling tools that can be used to drill at depths of 10,000 m. To meet this goal, an all-metal screw motor that can be applied in ultra-deep wells is designed, then its deformation and structural design are studied. Through numerical simulation, the change in clearance of the motor after expansion in high-temperature environments and the characteristics of deformation in ultra-deep well environments are analyzed. The results show that the metal screw motor has good performance and stability. The maximum deformation is less than 0.3 mm at depths of 9000~15,000 m in ultra-deep wells. The minimum design clearance should be greater than 0.2 mm to ensure that the stator and rotor remain engaged. The results of this research are expected to provide theoretical guidance for the design of all-metal screw motors for applications in ultra-deep well drilling projects to meet the demand for deep earth resource development.

In situ pressure-preserved coring (IPP-Coring) is one of the most efficient methods for identifying the scale of the oil and gas content. However, the differential motion assembly of the IPP-Coring system often undergoes ball and ball seat seal failure and sticking due to surface erosion, and a greater pressure drop may unexpectedly trigger the assembly. This paper addresses these issues by improving the hydraulic structure of an assembly based on a deep understanding of the flow characteristics in the assembly, thus increasing the success rate of the IPP-Coring. Computational fluid dynamics (CFD) was employed to investigate flows in a differential motion assembly. The effects of the diameter and outlet structure of the ball seat on the fluid status, velocity, and pressure distribution were thoroughly analyzed. When the ball seat diameter increased from 30 to 40 mm, the maximum velocity and pressure drop decreased to 0.55 and 0.2 times their original values, respectively. There was a severe vortex area in the differential motion assembly due to the presence of the ball seat, but changing the outlet structure in the ball seat to an arc structure decreased the length of the vortex area and the fluid velocity near the wall to 0.7 and 0.4 times, respectively, compared with those with the original right-angled structure. In addition, the pressure drop decreased to 0.33 times the original value. Thus, the hydraulic structure of the assembly was improved, and a 40 mm diameter ball seat and an arc-shaped ball seat outlet were selected. Particle trajectory and erosion calculation results showed that the improved structure has a lower particle velocity and less impact on the wall, and the average erosion rate is only 0.42 times the value of the original structure. Due to the better erosion resistance and smaller pressure drop, the improved structure shows promise for field performance.